eChapter Name: Effects of Industrial Effluents
9789390512546
eBook Name: RECYCLING OF INDUSTRIAL EFFLUENTS
by R. Manivanan
9.1 Introduction
The sources and types of chemical pollution to which freshwater systems can be exposed are many and varied. The origins of pollutants entering these systems range from those that are predominantly point sources (i.e., industrial effluents) to those that are mainly diffuse, such as agricultural run-off and acid deposition. Some of these are effectively continuous, whereas others are intermittent or episodic.
Pollutants can also be characterized by their quality: general organic loading, specific organic toxicants, inorganic toxicants, and acids. While most of the sources listed above produce mixtures of these characteristics, particular components are enhanced. Industrial effluents generally are the source of specific toxicants, but might also lead to general organic loading.
Some consideration should also be given to the types of system exposed to these pollutants. Most freshwater systems flow, but some more rapidly than others; that is, lakes and ponds have a slow throughput, the so called lentic systems whereas that for rivers and streams is rapid. Because they flow rapidly, the so-called lotic systems have been used for the transport of materials, such as removing industrial pollutants from factories and organic effluents from sewage works.
A view exists that lotic systems that depend substantially on organic inputs from terrestrial ecosystems as a basis for their economy should have the capacity for self-cleansing of at least organic pollutants. However, this perception has been challenged recently (Royal Commission on Environmental Pollution, 1992). Of course, “still” or so-called lentic waters may also be important repositories of pollutants, and are certainly exposed to diffuse inputs from agricultural land leading to eutrophication.
Thus, the challenge for aquatic ecotoxicology is to develop methods that can not only assess but also estimate the ecological impact of chemicals on a variety of complex ecosystems under diverse and complicated circumstances (e.g., periodic perturbations or steady trickles, and mixtures of varying complexity). The predictive approach is important in risk assessment used in the regulation of chemical pollutants. Assessment, at times referred to as a “retrospective approach,” is used to determine whether particular contaminants have an impact on specified natural ecosystems. This chapter reviews current methods, first predictive and then retrospective approaches, to address such problems. Initially, one must define what is to be measured, for it has relevance to both approaches.